• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.377-385
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• 2003

Flexural characteristics of the R.C beams strengthened with newly-developed grid-type carbon fiber plastics(CFRP-GRIDS) were investigated. The tests were conducted under the four-points load to the failure to investigate the strengthening effects of CFRP-GRIDS on the beams. Results showed that initial cracks appeared in the boundary layers of fibers embedded in the newly-placed mortar concrete slowly progressed to the direction of supports and showed fracture of fiber plastics and brittle failure of concrete in compression in sequence after the yielding of steel reinforcement. Accordingly, the appropriate area of Grid-type carbon-fiber plastics in the strengthening design of deteriorated RC structures should be limited and given based on the ultimate strength design method to avoid the brittle failure of concrete structures.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.44 no.4
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• pp.85-90
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• 2012

Wet pressing process has great influence not only on the paper properties but also on the efficiency of total manufacturing process including energy efficiency. The slow drainage propensity of old corrugated container(OCC) might require more complicated control of wet pressing process. In this study, the change in press efficiency and in structure of wet sheet by the various condition of laboratory roll press simulator were evaluated to provide background information about wet pressing of OCC. The higher pressure and the slower machine speed resulted in higher efficiency of wet pressing but the change trends of dryness depending on the wet press pressure and machine speed were shown differently according to OCC treatment. The effects of water contents of felt on the wet press efficiency and sheet structure were also investigated. The higher contents of water in felt resulted in less removal of water generally and the crushed structure of wet sheet were appeared especially at higher pressure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.63-64
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• 2012

A pyrotechnic actuated device (PAD) is a component that delivers high power in remote environments by combustion of a self-contained energy source. Historically, the design of these devices has been largely empirical and considered to be an art. In this study, an overview for developing an analytical model is introduced that efficiently evaluates performance of PAD. The model is integrated by three parts of different disciplines that are coupled in sequence with each other. First is the solid explosive burning to form product gas within an actuator and transport to an expansion chamber. Second is the insertion of initially tapered piston into a small hole by gas pressure in the chamber. Third is the shear cutting of the diaphragm from the piston to enable gas flow into the conduit. Some results of preliminary study for each of three parts are introduced in the presentation.

• Journal of the Korean Electrochemical Society
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• v.23 no.2
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• pp.47-55
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• 2020

Highly loaded LiCoO₂ positive electrodes are prepared to construct high-energy density lithium-ion batteries, their electrochemical performances are evaluated. For the standard electrode, a loading of about 2.2 mAh/㎠ is used, and for a high-loading electrode, an electrode is manufactured with a loading level of about 4.4 mAh/㎠. The content of carbon black as electronic conducting additive, and the porosity of the electrode are configured differently to compare the effects of electron conduction and ionic conduction in the highly loaded LiCoO₂ electrode. It is expected that the electrochemical performance is improved as the amount of the carbon black increases, but the specific capacity of the LiCoO₂ electrode containing 7.5 weight% carbon black is rather reduced. When the conductive material is excessively provided, an increase of electrode thickness by the low content of the LiCoO₂ active material in the same loading level of the electrode is predicted as a cause of polarization growth. When the electrode porosity increases, the path of ionic transport can be extended, but the electron conduction within the electrode is disadvantageous because the contact between the active material and the carbon black particles decreases. As the electrode porosity is lowered through the sufficient calendaring of the electrode, the electrochemical performance is improved because of the better contact between particles in the electrode and the reduced electrode thickness. In the electrode design for the high-loading, it is very important to construct the path of electron conduction as well as the ion transfer and to reduce the electrode thickness.

• Transactions of the Korean hydrogen and new energy society
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• v.10 no.4
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• pp.225-232
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• 1999

The $Mg_2Ni$ hydrogen storage alloys which have much higher theoretical discharge capacity than $AB_5$ and $AB_2$ type alloys were synthesized by mechanical alloying with some additives and subjected to the electrochemical measurements. Two different processes were employed to the synthesis of $Mg_2Ni$ alloys with using the high energy ball mill SPEX 8000. One was only ball milling, 12 hrs, the Mg and Ni powders for 12 hrs with additives such as $AB_5$, Ni, Co and Cu powders. In the other process the Mg and Ni powders were ball milled for 1 hr first and then heat treated at $300{\sim}400^{\circ}C$ for 1 hr to get $Mg_2Ni$ alloy, and finally the $Mg_2Ni$ alloy powders were ball milled with the additives for 12 hrs. The alloy powders prepared were compacted at room temperature under $7.64tons/cm^2$ into disk type electrodes for the electrochemical measurements. The experimntal results showed that the electrodes prepared with the heat treated alloy powders had a higher discharge capacities than those without heat treatment. The addition of Ni caused an increase of the discharge capacity and the addition of Co improved the cycling characteristics. The electrode prepared by ball milling of $Mg_2Ni$ and 10wt% Ni powders has showed the highest discharge capacity, 546mAh/g.alloy, which was 55% of the theoretical capacity.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.1
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• pp.31-37
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• 2007

A $^{192}Ir$ small-focal source has been developed by using the HANARO reactor and the radioisotope production facility at the Korea Atomic Energy Research Institute (KAERI). The small-focal source with the dimension of 0.5 mm in diameter and 0.5 mm in length was fabricated as an aluminum-encapsulated form by a specially designed pressing equipment. For the estimation of the radioactivity, neutron self-shielding and ${\gamma}-ray$ self-absorption effects on the measured activity was considered. From this estimation, it is realized that $^{192}Ir$ small-focal sources over 3 Ci activities can be produced from the HANARO. Field performance tests were performed by using a conventional source and the developed source to take images of a computer CPU and a piece of a carbon steel. The small-focal source showed better penetration sensitivity and geometrical sharpness than the conventional source does. It is concluded from the tests that the focal dimension of this source is small enough to maximize geometrical sharpness in the image taking for the close proximity shots, pipeline crawler applications and contact radiography.

• The Korean Journal of Food And Nutrition
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• v.19 no.4
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• pp.358-365
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• 2006

To study simultaneous water and solute transport kinetics during soaking in concentrated solution, the influence of the concentration and molecular weight of the solute(polyethylene glycol(PEG) and NaCl) in the soaking solution and the temperature on the water loss and solute gain rates were observed by using a model vegetable tissue(potato). When potato slices$(4cm{\times}4cm{\times}0.1cm)$ soaked in 60% PEG solutions, the water loss rate of the early phase decreased with increasing of the molecular weight of PEG from 200 to 6,000, while the final water loss increased with increasing the molecular weight of PEG and it reached to 80%. The cell wall of potato tissue was permeable to NaCl and PEGs of which average molecular weight is smaller than 400 but it was not permeable to PEG 600 and larger molecules. PEG which has average molecular weight below 600 induced plasmolysis and those above 600 induced cytorrhysis. The water loss rate of potato sample soaked in smaller molecular weight PEG solution was faster than those soaked in higher molecular weight PEG solution before cytorrhysis happened. The water loss rate was reversed after cytorrhysis happened. The volume change of potato within the first 60 minutes was larger in low molecular PEG solution but the final ratio of decreasing volume was larger in high molecular PEG solutions. In PEG 200 solution, the potato tissue was slightly shrinked without shape change. However, in PEG 4,000 solution, volume of potato was reduced significantly and potato tissue was twisted.

• Restorative Dentistry and Endodontics
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• v.36 no.4
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• pp.313-323
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• 2011

Objectives: This study investigated the optimal combination of 3-component photoinitiation system, consisting of CQ, p-octyloxy-phenyl-phenyl iodonium hexafluoroantimonate (OPPI), and 2-dimethylaminoethyl methacrylate (DMAEMA) to increase the degree of conversion of resin monomers, and analyze the effect of the ratio of the photoinitiator to the co-initiator. Materials and Methods: Each photoinitiators (CQ and OPP) and co-initiator (DMAEMA) were mixed in three levels with 0.2 wt.% (low concentration, L), 1.0 wt.% (medium concentration, M), and 2.0 wt.% (high concentration, H). A total of nine groups using the Taguchi method were tested according to the following proportion of components in the photoinitiator system: LLL, LMM, LHH, MLM, MMH, MHL, HLH, HML, HHM. Each monomer was polymerized using a quartz-tungsten-halogen curing unit (Demetron 400, USA) for 5, 20, 40, 60, 300 sec and the degree of conversion (DC) was determined at each exposure time using FTIR. Results: Significant differences were found for DC values in groups. MMH group and HHM group exhibited greater initial DC than the others. No significant difference was found with the ratio of the photoinitiators (CQ, OPPI) to the co-initiator (DMAEMA). The concentrations of CQ didn't affect the DC values, but those of OPPI did strongly. Conclusions: MMH and HHM groups seem to be best ones to get increased DC. MMH group is indicated for bright, translucent color and HHM group is good for dark, opaque colored-resin.

• Journal of the Korean Society of Food Science and Nutrition
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• v.34 no.10
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• pp.1559-1565
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• 2005

The Purpose of this study was to investigate college students' attitude toward body weight control, health-related lifestyle and dietary behavior by their perception on body image and obesity index. The subjects were 871 nation- wide college students (330 male and 541 female students) participating in a nutritional education program via internet- A cross-sectional survey was conducted using a self-administered questionnaire via internet. The data were analyzed by a SPSS 10.0 program. Height and weight (p < 0.05), and the distribution of obesity index (p < 0.001) showed significant differences between male and female college students. As for self perception on body image, the necessity of body weight control and the experience of efforts to change the body weight, there were significant differences between male and female college students (p < 0.001). There were significant differences among groups by obesity index in the hours of exercise (p < 0.01), drinking (p < 0.01) and smoking (P < 0.001). As for methods of body weight control, all the groups by obesity index thought that program of body weight control by diet company is the most desirable method. Therefore, we must recognize that it is hard to correct health problems resulting from wrong lifestyle and dietary behavior fixed during college life and prepare a system for college students to obtain correct lifestyle and dietary behavior.

• Journal of Radiation Protection and Research
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• v.10 no.2
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• pp.96-108
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• 1985

A study for the assessment of natural environmental radiation exposure at a flat and open field of about $10,000m^2$ in area in CNU Daeduk campus has been carried out by means of gamma-ray scintillation spectrometry and thermoluminescence dosimetry for one year period of time from October 1984. The detectors used were 3'${\phi}{\times}$3' NaI(T1) and two different types of LiF TLD, namely, chip sealed in plastic sheet which tightly pressed on two open holes of a metal plate and Teflon disk. Three 24-hour cycles of in-situ spectrometry, and two 3-month and one 1-month cycles of field TL dosimetry were performed. All the spectra measured were converted into exposure rate by means of G(E) opertaion, and therefrom exposure rate due to terrestrial component of environmental radiation was figured out. Exposure rate determined by the spectrometry was, on average, $(10.54{\pm}2.96){\mu}R/hr$, and the rates of $(12.0{\pm}3.4){\mu}R/hr$ and $(11.0{\pm}3.6){\mu}R/hr$ were obtained from chip and disk TLD, respectively. Fluctuations in diurnal variation of the exposure rate measured by the spectrometry were noticeable sometime even in a single cycle of 24 hours. It is concluded that appropriately combined use of TLD with iu-sitn gamma-ray spectrometry system can give more accurate and precise measure of environmental radiation exposure, and further study for more adequate and sensitive TLD for environmental dosimetry, including improvement and elevation of accuracy in data assessment through inter-laboratory or international intercomparison is necessary.